This buttercream is an old-fashioned American powdered sugar and butter frosting. Be sure to beat the icing for the amount of time called for in the recipe to achieve the desired creamy texture. I have adapted this from Magnolia Bakery.
FROSTING, ICING, ETC RECIPE HELP

INGREDIENTS
1 cup (2 sticks) unsalted butter, slightly softened
6 to 8 cups powdered sugar, sifted; sift after measuring 
1/2 cup whole or 2% milk
2 teaspoons vanilla extract

INSTRUCTIONS
Cut each stick of butter into quarters and place in a large mixing bowl. Turn on the mixer, fitted with a paddle attachment, to low and slowly add four cups of the sugar at the side of the bowl. Stir the vanilla into the milk. Slowly drizzle the milk at the side of the bowl,

Increase the mixer speed to medium and beat until smooth and creamy, about 4 to 5 minutes.

Lower the mixing speed to low and gradually add the remaining powdered sugar at the side of the bowl, 1 cup at a time, and beat well after each addition, until the icing is thick enough to be of spreading consistency; you may not need all of the sugar. Increase the mixer speed to medium and beat for 2 minutes until thick and creamy. Add more powdered sugar if necessary. or more milk to correct.

To tint icing, add a few drops of food coloring and mix thoroughly.

STORAGE
Use and store the icing at room temperature because icing will set if chilled. Icing can be stored in an airtight container for up to 3 days. 

VARIATIONS If you are icing a 3-layer cake, use the following recipe proportions:
INGREDIENTS
1 1/2 cups (3 sticks) unsalted butter
8 to 10 cups confectioners' sugar
3/4 cup milk
1 tablespoon vanilla extract
INSTRUCTIONS
Follow the instructions above.

Recipe adapted from More From Magnolia by Allysa Torey